Contents

Introduction

The Garcia mobile robot is a great vehicle for moving sensors around a laboratory environment.  In this guide, the process of building an interface cable for a Hokuyo URG-04LX scanning laser range finder to communicate with an embedded host processor is outlined.  Wire lengths are recorded to fit neatly inside a Garcia robot. 

Step 1: Modifying an Acroname Serial Interface Connector

The Hokuyo URG-04LX outputs data at RS232 signal levels.  Many embedded controllers have additional serial ports, but require signals to be at CMOS or TTL levels for proper operation.  An Acroname Serial Interface connector is very useful device that is designed to bridge RS232 levels to CMOS compatible levels. 

A dremel tool is used to cut away the DB9 connector so there is easy access to the solder pads for the RS232 signals.  Carefully cut near the plastic housing and the solder cups.  Once the connector is removed, one can clean away the solder cups from the circuit board using some solder braid. 

Dremel away the DB9 connector

The 4 position connector will also need to be removed from the circuit board.  Cut away the connector leads and clean out the through holes. 

Once both connectors are cleared away, set the board circuit board aside for the moment. 

Step 2: Modify the Hokuyo Serial Cable

Cut the included the serial cable to 23.5 inches in length. 

Ideal cable length

Once the wire is cut to length, carefully strip approximately 2 inches of the black insulation away from the cable.  Remove the strings and cut the black, white and red wires. 

Strip away the black sheilding insulation

Step 3: Solder URG-04LX Wires to Serial Adapter

Solder the laser's Rx (yellow), Tx (green) and GND (dark purple) wires to the modified serial interface connector. 

Solder the laser serial wires to the interface adapter.

Step 4: Build Male Serial Extension Cable

The TTL serial data lines get built into a serial interface connector based on the Acroname Serial Interface Standard.  A C10-SER-INT-CONN-EXT extender is used for convenience.  The C10 cable is cut in half and both ends will be used. 

On the male connector side, remove the red wire that is typically used for passing VCC along.  Then take the yellow and green wires and solder them to the through holes on the modified serial interface connector as shown in the following figure. 

Building a male serial cable extension

Step 5: Power Cable Construction

Use the remaining half of the C10-SER-INT-CONN-EXT for supplying power to the modified serial interface connector.  Remove the remaining yellow and green wires.  Only the black and red wires should remain. 

Also, solder a 1 inch piece of black and red wires to the modified serial interface connector in the remaining through holes as shown in the following figure. 

Solder short power extension wires to the serial interface connector.

Step 6: Combining Ground Wires

Solder all the black and blue wires together.  Before soldering be sure to place a small piece of heatshrink over the exposed wires that get soldered together. 

Join all the ground wires together.

Step 7: Join the Power Wires

Solder all the red and brown wires together.  Before soldering be sure to place a small piece of heatshrink over the exposed wires that get soldered together. 

Join all the power wires together.

Step 8: Test and Finish the Cable

Test the cable by using a host computer and communicating down a serial port to the laser.  Once you get data coming from the laser, melt the heatshrink around the power and ground wires. 

As a final finishing touch, place the entire assembly inside some 3/4 inch clear heatshrink.  Melt the heatshrink, zip tie the cables together and you should now have a cable that converts the laser range finder data to CMOS levels. 

Revision History:

• 2007-09-11: New Instructional Guide
• 2007-09-13: Fixed a wiring mistake when joining the power wires together.

Related Links:

Acroname Serial Interface Standard